Bipolar junction transistors are active semiconductor devices formed by a pair of P-N junctions, including an emitter-base junction and a collector-base junction. An NPN bipolar junction transistor has a thin region of P-type material providing the base region between two regions of N-type material providing the emitter and collector regions. A PNP bipolar junction transistor has a thin region of N-type material providing the base region between two regions of P-type material constituting the emitter and collector regions. The movement of electrical charge carriers which produces electrical current flow between the collector region and the emitter region is controlled by an applied voltage across the emitter-base junction.
Conventional vertical NPN bipolar devices used for electrostatic discharge (ESD) protection of other devices typically include an n-buried layer (NBL) together with a N+ sinker diffusion as collectors in each device stripe to provide a low resistance-path to carry ESD strike induced current back to the top surface of the substrate (e.g., a top silicon surface). Due to the large lateral diffusion of the N+ sinker diffusion when forming the N+ sinker using an ion implant followed by a thermal diffusion of the dopant to reach a depth of several μms to provide a low resistance connection to the NBL, the device pitch is thus limited to a large dimension, resulting in the need for significant area on the integrated circuit (IC) die.